In recent years, biodegradable plastics have been actively developed as materials that can solve problems caused by plastic waste that places a heavy burden on the global environment, such as impact on the ecosystem, generation of harmful gases during combustion, and global warming due to a large amount of heat generated by combustion.
In particular, carbon dioxide generated by combustion of plant-derived biodegradable plastics was originally present in the air, and therefore the amount of carbon dioxide in the air does not increase. This is referred to as carbon neutral, and regarded as important under the Kyoto Protocol that sets carbon dioxide reduction targets. For this reason, biodegradable plastics have been expected to be actively used.
Recently, from the viewpoint of biodegradability and carbon neutral, aliphatic polyester resins, especially polyhydroxyalkanoate (hereinafter, sometimes referred to as PHA) resins have received attention as plant-derived plastics. Among PHA resins, for example, poly(3-hydroxybutyrate) homopolymer resins (hereinafter, sometimes referred to as P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer resins (hereinafter, sometimes referred to as P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resins (hereinafter, sometimes referred to as P3HB3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer resins (hereinafter, sometimes referred to as P3HB4HB), and polylactic acid (hereinafter, sometimes referred to as PLA) have received attention.
However, the PHA resins are originally poor in impact strength and tensile elongation, and therefore need to be improved.
Patent Literature 1 discloses a thermoplastic resin composition comprising a polylactic acid-based resin and a graft copolymer using a polyorganosiloxane/acrylic composite rubber containing a polyorganosiloxane and an alkyl(meth)acrylate rubber. However, the resin composition does not have sufficient impact strength.
Patent Literature 2 discloses that the melt strength of an aromatic polyester can be improved by adding a highly-dispersible high-molecular-weight vinyl aromatic copolymer. However, the obtained polyester resin composition is not preferred from the viewpoint of carbon neutral.
Patent Literature 3 discloses that the molding processability of a polyester, which is a thermoplastic polymer, in vacuum forming, pressure forming, or the like can be improved by blending with an acrylic compound. However, in Patent Literature 3, examples of the polyester do not include a polyhydroxyalkanoate that is a biodegradable aliphatic polyester-based resin.
Further, the PHA resins have a low crystallization speed, and therefore require a long cooling time for solidification after heat melting in molding processing, which causes a problem that productivity is poor.
Therefore, it has heretofore been proposed that an inorganic material, such as boron nitride, titanium oxide, talc, layered silicate, calcium carbonate, sodium chloride, or a metal phosphate, is blended with a PHA resin to improve crystallization. However, its effect is insufficient.